In order to fixedly fit a shaft-like metal member into an annular portion of a housing formed of metal, a holder portion is integrally formed along the outer peripheral edge of the shaft-like metal member, and the holder portion is fastened to the housing by a bolt. However, the weight and cost of the member increase because the holder portion is formed. Furthermore, the productivity for mass production is low because bolting is carried out. Accordingly, a method of coupling metals by plastically deforming the metals is known (see Patent Document 1, for example).